The present invention relates to a semiconductor laser driver circuit for reducing laser noise through its multimode oscillation with a high frequency current superposed, more particularly, it relates to a semiconductor laser driver circuit suitably adapted to an optical information processing device which is recordable or erasable and oscillates a semiconductor laser with a high output when it is recorded or erased.
Semiconductor lasers have been typically used as a light source of an optical information processing device such as an optical disk, an optical printer, etc. With the development of the transverse mode control technique of the semiconductor lasers, many semiconductor lasers which oscillate in a primary transversal mode and uniform longitudinal mode have appeared. Such semiconductor lasers, when incorporated in the optical information processing device, however, have had a problem, because of their improved coherency, that when the outgoing light from the semiconductor laser reflects from the edge surface of an optical component or the disk surface to be fed back to the laser, a noise (feedback noise) is disadvantageously generated. This noise is attributable to the fact that the very coherent lights, i.e., the outgoing light and reflecting light, interfere with each other so that the oscillation longitudinal mode of the laser becomes unstable because of its jump or multi-longitudinal mode oscillation. The oscillation longitudinal mode also becomes unstable due to the temperature range. This is because the temperature change shifts the wavelength at a single-longitudinal-mode oscillation continuously and also in a discrete jumping manner. The noise is generated when that wavelength jumps. The noises thus generated may degrade signal-to-noise ratios in the signals in the optical communication or optical disk devices.
In order to reduce the noises, there has been proposed a method for driving the laser at a high frequency by providing a high frequency oscillator in a laser driver circuit, as disclosed in U.S. Pat. No. 4,480,325. This method using high frequency driving intends to reduce the laser noise in the case of the D.C. driving in which the high frequency modulation is continuously modulated.